It's a big treadmill.
I think I'm getting the hang of it, though. I had a book release last week and I'm not panicking about promo. I'm doing one bit of promo every day (post to a loop, post something about the book, etc.). I figure I'm in this for the long haul, and if it doesn't sell big today, it might sell steadily.
This is so not what I thought publishing would be. I think I had that idea, "publish the book, sit back and wait for accolades."
Nope. Even if the book is loved by some, it's panned by others.
Just keep writing. That's all you can do. And enjoy the ride, because it's all part of the big picture.